1. Field of the Invention
The invention concerns a method for producing a controlled atmosphere having an oxygen partial pressure of below 10.sup.-13 Pa and an operating temperature above 1000.degree. C. The invention also refers to a device for implementing this method.
2. Description of Related Art
An atmosphere having a low oxygen partial pressure and high temperature is often requested for studies relating to the corrosion behaviour of advanced materials. Thus, in the frame of coal gasification, which takes place at temperatures between 1200.degree.C. and 1400.degree. C., the refractory lining of the coal gasifier is in contact with gases such as CO, CO.sub.2, H.sub.2 S, H.sub.2, COS, ammonia at very low oxygen partial pressure. In most of today's industrial coal gasifiers the oxygen partial pressure lies below 10.sup.-10 Pa. The evaluation of the corrosion behaviour of such materials in a laboratory requires gas mixtures in which the partial pressures of the most important components such as oxygen (p.sub.o2) and sulphur (p.sub.s2) should be adapted to the real conditions of an industrial coal gasifier. It is particularly difficult to ensure in the laboratory an oxygen partial pressure which corresponds to that in a coal gasifier particularly if the oxygen partial pressure lies below 10.sup.-13 Pa. This is due to the fact that the other components of the gas mixture are seldom available free of oxygen impurities and that neither the admission duct for the mixture to the furnace nor the furnace itself is free of oxygen. In fact, there exist components in the furnace made for example of aluminium oxide which release oxygen at high temperature.
A possible solution to this problem for obtaining a defined atmosphere having a very low oxygen partial pressure is to conceive special furnaces with a graphite lining. However, this solution has certain drawbacks:
1. A special furnace is required for tests under a very low oxygen partial pressure (high investment).
2. Such graphite furnaces must exclusively be used for tests under extremely low oxygen partial pressures, as otherwise the graphite lining will oxidise.
From U.S. Pat. No. 3,732,056 an apparatus is known for hot pressing of oxide ceramics in a controlled oxygen atmosphere. This apparatus intends to increase the oxygen content in the furnace for oxidizing the ceramic material and not to reduce the oxygen content in a gas mixture to values which could not be achieved according to the state of the art.
The state of the art may be found in U.S. Pat. No. 5,340,553 since the method disclosed in this document concerns the removal of oxygen from a controlled atmosphere. This is achieved by a silicon material which is heated in a furnace up to about 1000.degree. C. and acts as a getter which absorbs oxygen. However, no final partial oxygen pressure values are disclosed in this document.